Electrical connection element

ABSTRACT

Electrical connection element containing a copper-zinc alloy. The copper-zinc alloy comprises (in percent by weight): 28.0 to 36.0% Zn, 0.5 to 1.5% Si, 1.5 to 2.5% Mn, 0.2 to 1.0% Ni, 0.5 to 1.5% Al, 0.1 to 1.0% Fe, optionally also up to a maximum of 0.1% Pb, optionally also up to a maximum of 0.1% P, optionally up to a maximum of 0.08% S, the remainder being Cu and inevitable impurities. According to the invention, mixed silicides containing iron, nickel and manganese are incorporated in the matrix. The structure comprises an α-matrix, which contains inclusions of β-phase from 5 up to 45 percent by volume and of mixed silicides containing iron, nickel and manganese up to 20 percent by volume. The structure further comprises mixed silicides containing iron, nickel and manganese having a stemmed shape and iron and nickel enriched mixed silicides having a globular shape.

The invention relates to an electrical connection element containing a copper-zinc alloy as per the preamble of claim 1.

Numerous new automobile applications for safety, comfort and power can be realized only by the targeted use of electronic functions and components. Owing to the increasing demands made of the plug connectors and thus of the materials used, there has in recent years been a discernible trend toward high-performance copper alloys. These precipitation-hardening copper materials display high mechanical strength, high conductivity and good deformability. Proceeding from the first generation of the HP—Cu alloys, for example CuNi3SiMg having an electrical conductivity of a little above 20 MS/m, the property combination of high strength and high conductivity needs to be optimized further.

A step in this direction was firstly the development of precipitation-hardening copper alloys, for example based on the system CuCrAgFeTiSi with 46 MS/m and strengths up to 610 MPa. A further significant advantage of this alloy is the very good relaxation resistance of the material when used at elevated temperatures up to 200° C. This type of alloy is able to cover applications in the fields of automotive industry, industrial electronics and telecommunications.

In addition, bronze materials which have a fine microstructure having a grain size of not more than 3 μm are used. In this way, significantly high mechanical strengths combined with greatly improved deformation properties are achieved. As a result of the significantly improved deformability, processors can achieve correspondingly small bending radii. Likewise, the improved bendability means that the roughness in the deformation zones is significantly lower than when using standard bronzes. Subsequent coatings can thus be made with a lower layer thickness, by means of which considerable cost savings in further processing can be achieved. The electrical conductivity is identical to that of standard bronzes and is from about 7.5 to 12 MS/m.

A further precipitation-hardening CuNi1CoSi alloy comprising Ni—Co mixed silicides is likewise very well suited to economical miniaturization of plug connectors. The material has high strength, has a comparatively good electrical conductivity of 29 MS/m and a comparatively good thermal conductivity and can be processed readily.

The materials described are, in particular, suitable for processing on automatic stamping/bending machines and can be worked by cutting machining only with great difficulty.

Further copper materials in the form of rods and wires which are outstandingly suitable for bushes and pins to be produced by cutting machining for plug connectors are also known in the materials portfolio of inexpensive brass materials with the alloys CuZn37Pb0.5, CuZn35Pb1, CuZn35Pb2, CuZn37Pb2, CuZn36Pb3 and CuZn39Pb3, which are used for demanding applications in the production of turned plug connectors.

Depending on the technical requirements, materials having a high electrical conductivity, high mechanical strength and both these properties in combination are used in these cases. Thus, CuPb1P is also a further readily machineable automatic machine material which at the same time has a high electrical conductivity of about 50 MS/m. It is particularly suitable for plug connectors and other electronic applications.

Apart from the mixed crystal-hardening alloys, the alloy spectrum is rounded off by further precipitation-hardening materials. These include, for example, CuNi1Pb1P and CuNiPb0.5P as low-alloy copper material having a high strength, good conductivity of at least 32 MS/m and also good cutting machineability. The material is, due to the Pb content, particularly suitable for plug contacts produced by cutting machining in electrical engineering and electronics.

High strengths with corresponding spring properties can also be obtained using the multicomponent tin bronze CuSn4Zn4Pb4P containing 4% of each of tin, zinc and lead. This tin bronze is readily cold formable and can be worked by cutting machining very well. Specific fields of use are springy electronic contacts.

Aspects which now always have to be taken into account in alloy development are the various environmental directives and restrictions in terms of material. In addition, there are further development potentials for alternative or supplementary alloys which disclose property combinations suitable for plug connectors. Here, not only the physical properties but especially also good workability play a critical role.

It is an object of the invention to provide an electrical connection element composed of a low-lead or lead-free copper alloy.

The invention is defined by the features of claim 1. The further claims referring back to claim 1 define advantageous embodiments and further developments of the invention.

The invention includes the technical teaching for construction of an electrical connection element containing a copper-zinc alloy. The copper-zinc alloy consists of (in % by weight):

from 28.0 to 36.0% of Zn,

from 0.5 to 1.5% of Si,

from 1.5 to 2.5% of Mn,

from 0.2 to 1.0% of Ni,

from 0.5 to 1.5% of Al,

from 0.1 to 1.0% of Fe,

optionally up to not more than 0.1% of Pb,

optionally up to not more than 0.1% of P,

optionally up to 0.08% of S,

balance Cu and unavoidable impurities.

According to the invention, iron-nickel-manganese-containing mixed silicides are embedded in the matrix. The microstructure consists of an α matrix in which inclusions of β phase in a proportion of from 5 to up to 45% by volume and also of iron-nickel-manganese-containing mixed silicides in a proportion of up to 20% by volume are present. Furthermore, the iron-nickel-manganese-containing mixed silicides are present in rod-like form and also iron-nickel-enriched mixed silicides having a globular shape are present in the microstructure.

It has surprisingly been found that the alloy composition of the invention is suitable for electrical connection elements. Hitherto, use of such alloys was, according to the German first publication DE 10 2007 029 991 A1 of the applicant, envisaged only for use in sliding elements in internal combustion engines, gearboxes or hydraulic apparatuses. The content of this first publication is fully incorporated by reference into the present description. Such different applications pursue a different purpose of a property combination optimized for specific uses. A property combination of an increase in the strength, the heat resistance of the microstructure and the complex wear resistance combined with satisfactory toughness properties with a view to engine applications.

In contrast, the invention proceeds from the idea of providing an electrical connection element comprising a copper-zinc alloy comprising embedded iron-nickel-manganese-containing mixed silicides, which can be produced, in particular, by means of continuous or semicontinuous casting. Due to the mixed silicide formation and microstructure formation, the copper-zinc alloy has a very high electrical conductivity for this group of materials.

The alloy also has high hardness and strength values, but a required degree of ductility, expressed by the elongation at break in a tensile test, is nevertheless ensured. With this property combination, the subject matter of the invention is found to be particularly suitable for electrical connection elements, for example turned plug connectors, plug devices, electric clamps, optionally also with screw connections.

In the preceding production step of casting of the alloy, early precipitation of iron- and nickel-rich mixed silicides initially takes place. These precipitates can, during further growth, grow to form iron-nickel-manganese-containing mixed silicides having a considerable size and often a rod-like shape. Furthermore, a considerable proportion tends to remain small with a globular shape, which is present in finely dispersed form in the matrix. The finely dispersed silicides are considered to be the reason why stabilization of the β phase takes place. In particular, the alloy has a high ductility during cold forming. In the case of electrical connection elements, this is particularly important for crimping, during which the material is usually subjected to great plastic deformation. Thus, flanging, pinching or folding of the material with virtually any degree of deformation is possible without crack formation occurring in the material.

The material is also particularly suitable for electrical connection elements produced by cutting machining. The good cutting machineability is achieved even by a β phase of 5% by volume. At higher contents up to 45% by volume of β phase, the formation of shavings during cutting machining also improves as a result of the desirable formation of short shavings. At a proportion of β phase below 5% by volume, the cutting machineability is no longer satisfactory for high rates of removal of material in use as material on automatic machines. At a β phase content of above 45% by volume, it is found that the toughness of the material and the heat resistance of the microstructure decrease. The final state of the alloy from the respective manufacturing process leads to a β phase which is embedded as islands in a microstructure composed of an α matrix. Such islands of β phase are particularly advantageous for the cutting machineability and the corrosion resistance of the alloy.

However, a particularly high surface quality of the surfaces worked by cutting machining is achieved at a proportion of β phase of, in particular, from 10 to 25% by volume. Comparatively low tool wear is also obtained in the indicated volume range from 5 to 45% by volume of β phase, so that the tools have correspondingly long operating lives and the tool costs are thus reduced. Proportions of iron-nickel-manganese-containing mixed silicides above 20% by volume would bring about such a great hardness increase that the balance of advantageous properties of the material would suffer.

Particular mention may also be made of the relaxation resistance of the material, as a result of which the spring force of an electrical connection element is maintained.

The particular advantage of the alloy of the invention is thus based on a property combination optimized for the intended uses in the form of an increase in the strength, the heat resistance of the microstructure and the electrical conductivity combined with satisfactory toughness properties.

In addition, the claimed solution in respect of the material takes into account, owing to the replacement of the lead content compared to conventional alloys, the need for an environmentally friendly lead-free alloy alternative. Furthermore, this material is predestined for particular applications in which a necessary degree of plasticizability is acquired despite the demanding requirements in terms of the hardness and the strength.

In an advantageous embodiment of the invention, the copper-zinc alloy can contain

from 30.0 to 36.0% of Zn,

from 0.6 to 1.1% of Si,

from 1.5 to 2.2% of Mn,

from 0.2 to 0.7% of Ni,

from 0.5 to 1.0% of Al,

from 0.3 to 0.5% of Fe.

A particularly advantageous alloy composition is selected as a result of the narrower limits. The toughness properties and the electrical conductivity, optionally with a final annealing heat treatment, are improved further in this way. The final annealing heat treatment is preferably carried out at from 300° C. to 400° C. for from 3 to 4 hours.

In a further advantageous embodiment of the invention, the copper-zinc alloy can contain from 33.5 to 36.0% of Zn. At these relatively high zinc contents, the toughness properties required for electrical connection elements and good electrical conductivity can still be achieved. The proportion of the further elements, in particular the proportion of copper, is correspondingly reduced by a very high zinc content. As a consequence, the alloy has a correspondingly lower metal price due to a higher proportion of relatively cheap zinc.

The electrical conductivity of the alloy can advantageously be at least 5.8 MS/m. Particularly preferred conductivities are from at least 10 MS/m to above 13 MS/m. These values are not achieved by comparable materials such as the lead-containing brasses. Even values above 13 MS/m can be set by suitable further treatment steps.

The microstructure consisting of an α matrix in which inclusions of β phase in a proportion of from 5 to 45% by volume and of iron-nickel-manganese-containing mixed silicides in a proportion of up to 20% by volume are present can advantageously have been formed after further treatment comprising at least one hot forming and/or cold forming step and optionally further heat treatment steps. With the β inclusions and hard phases of differing size distribution in an α matrix, this alloy ensures advantageous heat resistance of the microstructure with satisfactory toughness properties for the production of the connection elements.

For the further treatment, the alloy can have advantageously gone through the following steps during its further treatment:

-   -   extrusion or hot rolling in the temperature range from 600 to         800° C.,     -   at least one cold forming step, preferably by drawing or cold         rolling.

In a preferred embodiment of the invention, the alloy can also have gone through the following steps in its further treatment:

-   -   extrusion or hot rolling in the temperature range from 600 to         800° C.,     -   a combination of at least one cold forming step, preferably by         drawing or cold rolling, and at least one heat treatment in the         temperature range from 250 to 700° C., preferably for a heat         treatment time of from 20 minutes to 5 hours. A fine dispersion         of the heterogeneous microstructure can be set by means of a         combination of cold forming by drawing and one or more heat         treatments of the starting materials in the form of round wires,         profiled wires, round rods, profiled rods, hollow rods and tubes         in the temperature range from 250 to 700° C. The requirement for         improvement of the electrical conductivity is addressed in this         way.

The relationship between the magnitude and distribution of the proportion of the β phase and the heat resistance of the microstructure is also of particular interest. However, since this body-centered cubic crystal type assumes an indispensible strength-increasing function in the copper-zinc alloys, the minimization of the β content should not be the exclusive focus. The phase distribution in the microstructure of the copper-zinc alloy can be modified by means of the manufacturing sequence extrusion or hot rolling/drawing or cold rolling/intermediate heat treatment so that the alloy has not only a high strength but additionally also a satisfactory heat resistance, ductility and good electrical conductivity.

In a preferred embodiment, the forming can be followed by at least one annealing heat treatment in the temperature range from 250 to 450° C. and preferably for a heat treatment time of from 2 to 5 hours during the further treatment.

During the course of manufacture, it is necessary to reduce the level of residual stresses by means of one or more annealing heat treatments. The reduction of the residual stresses is also important for ensuring a sufficient heat resistance of the microstructure and for ensuring a satisfactory straightness of the round wires, profiled wires, round rods, profiled rods, hollow rods and tubes as precursor products for the electrical connection elements.

Further working examples of the invention will be illustrated with the aid of tables. These concern an embodiment which is considered to be best after the studies. However, further, different embodiments are also suitable for achieving the inventive advantages in the context of the invention.

Cast pins composed of the copper-zinc alloy of the invention were produced by continuous casting or chill mold casting. The chemical composition of the continuous casting of the alloy 1 and of the chill mold casting of the alloys 2 and 3 is shown in Tab. 1.

TABLE 1 Chemical composition of the cast pins or cast blocks (in % by weight) without indication of possible impurities Cu Zn Si Mn Ni Sn Al Fe [%] [%] [%] [%] [%] [%] [%] [%] Alloy 1 64.0 31.1 1.0 2.0 0.6 <0.01 0.9 0.4 Alloy 2 64.0 30.8 1.1 2.1 0.6 — 0.9 0.5 Alloy 3 61.6 34.8 0.7 1.7 0.3 — 0.5 0.4

Manufacturing sequence 1:

-   -   Extrusion of the cast pins composed of alloy 1 to form tubes at         a temperature of 670-770° C.     -   Combination of cold forming/intermediate heat treatments         (630-700° C./50 min-3 h)/straightening/annealing heat treatments         (300-400° C./3 h).

After completed manufacture, the properties of the microstructure, the electrical conductivity and the mechanical properties of the tubes having the dimensions (30.1×24.7) mm are at the level shown numerically in Tab. 2.

TABLE 2 Properties of the microstructure, electrical conductivity and mechanical properties at two positions on the tubes in the final state (alloy 1) Elec- Elon- trical gation β Grain conduc- at Hard- content size tivity R_(m) R_(p0.2) break ness [%] [μm] [MS/m] [MPa] [MPa] A5 [%] HB 5 15-20 11.4 640 560 14.5 201 15-20 20-25 11.2 647 572 13.2 199

Manufacturing sequence 2:

-   -   Extrusion of the cast pins composed of alloy 1 to form round         rods at a temperature of 650-750° C.     -   Combination of cold forming/heat treatments (630-720° C./50         min-4 h)/straightening/annealing heat treatments (300-450°         C./2-4 h).

After completed manufacture, the properties of the microstructure, the electrical conductivity and the mechanical properties of the round rods having the diameter of 13.40 mm, 16.35 mm and 45.50 mm are at the level shown numerically in Tab. 3.

TABLE 3 Properties of the microstructure, electrical conductivity and mechanical properties of the round rods in the final state (alloy 1) Elec- Elon- trical gation Round β Grain conduc- at Hard- rods content size tivity R_(m) R_(p0.2) break ness Ø [mm] [%] [μm] [MS/m] [MPa] [MPa] A5 [%] HB 13.40 5   20-25 11.4 607 512 12.4 191 16.35 15-20 25 10.9 638 549 12.0 199 45.50 10-15 25 10.7 570 420 20.1 172

Manufacturing sequence 3:

-   -   Hot rolling of the cast blocks composed of alloys 2 and 3 to         form rolled sheets at a temperature of 650-730° C.     -   Cold rolling of the sheets with a deformation of from 15 to 25%         optionally with annealing heat treatments (300-450° C./2-4 h)

In addition, optionally milling of the surfaces between the individual process steps.

TABLE 4 Properties of the microstructure, electrical conductivity and mechanical properties of the rolled sheets in the final state (rolled sheet thickness 3 mm, with and without annealing heat treatment AHT as last process step) Elec- Elon- trical gation β Grain conduc- at Hard- content size tivity R_(m) R_(p0.2) break ness Alloy [%] [μm] [MS/m] [MPa] [MPa] A5 [%] HB Alloy 2 14 15-20 8.9 608 540 7.8 188 (without AHT) Alloy 2 13 15-20 10.5 646 543 15.6 192 (AHT 340° C./3 h) Alloy 2 13 15-20 10.7 615 483 19.0 184 (AHT 400° C./3 h) Alloy 3 20 20-25 11.0 596 516 11.3 178 (without AHT) Alloy 3 18 20-25 12.7 593 464 18.6 176 (AHT 340° C./3 h) Alloy 3 18 20-25 12.7 580 428 21.6 170 (AHT 400° C./3 h)

Manufacturing sequence 4:

-   -   Hot rolling of the cast blocks composed of alloys 2 and 3 to         form rolled sheets at a temperature of 650-730° C.     -   Combination of a heat treatment (650° C./3 h) and cold rolling         of the sheets with a deformation of from 15 to 25% optionally         with annealing heat treatments (300-450° C./2-4 h)

In addition, optionally milling of the surfaces between the individual process steps.

TABLE 5 Properties of the microstructure, electrical conductivity and mechanical properties of the rolled sheets in the final state (rolled sheet thickness 3 mm, with and without annealing heat treatment AHT as last process step) Elec- Elon- trical gation β Grain conduc- at Hard- content size tivity R_(m) R_(p0.2) break ness Alloy [%] [μm] [MS/m] [MPa] [MPa] A5 [%] HB Alloy 2 10 10-15 9.3 573 510 11.8 180 (without AHT) Alloy 2 10 10-15 10.6 587 470 19.4 176 (AHT 340° C./3 h) Alloy 2 10 10-15 10.6 583 452 20.0 174 (AHT 400° C./3 h) Alloy 3 15 20-25 10.5 555 482 13.5 172 (without AHT) Alloy 3 15 20-25 12.7 553 422 21.0 166 (AHT 340° C./3 h) Alloy 3 15 20-25 12.7 544 403 19.5 162 (AHT 400° C./3 h)

Manufacturing sequence 5:

-   -   Hot rolling of the cast blocks composed of alloys 2 and 3 to         form rolled sheets at a temperature of 650-730° C.     -   Combination of cold rolling of the sheets with a deformation of         from 15 to 65%/heat treatments (630-720° C./50 min-4 h)

In addition, optionally milling of the surfaces between the individual process steps.

TABLE 6 Properties of the microstructure, electrical conductivity and mechanical properties of the rolled sheets in the final state (rolled sheet thick- ness 2.3 mm, without annealing heat treatment AHT) Elec- Elon- trical gation β Grain conduc- at Hard- content size tivity R_(m) R_(p0.2) break ness Alloy [%] [μm] [MS/m] [MPa] [MPa] A5 [%] HB Alloy 2 10 10-15 9.1 558 484 17.6 171 Alloy 3 15 15-20 10.2 556 471 18.9 167

The value of the electrical conductivity in particular can be increased further for the formats of the alloys 2 and 3 produced according to the manufacturing sequence 5 by an additional annealing heat treatment at a temperature of from 250 to 450° C.

With regard to the working examples, it may be emphasized that the β content is in the range 5-20% in the case of all five manufacturing sequences. Further studies show that the β contents are preferably in the range 5-30%. The island-like formation of the β phase in the final state of manufacture, embedded in a microstructure composed of an α matrix, can be somewhat more or less pronounced. At increasingly low contents of β phase, isolated islands are likely to form and in the limiting case can form a type of filling of interstices relative to the crystallites of the α matrix. 

1. An electrical connection element containing a copper-zinc alloy consisting of (in % by weight): from 28.0 to 36.0% of Zn, from 0.5 to 1.5% of Si, from 1.5 to 2.5% of Mn, from 0.2 to 1.0% of Ni, from 0.5 to 1.5% of Al, from 0.1 to 1.0% of Fe, optionally up to not more than 0.1% of Pb, optionally up to not more than 0.1% of P, optionally up to 0.08% of S, balance Cu and unavoidable impurities, characterized in that iron-nickel-manganese-containing mixed silicides are embedded in the matrix, in that the microstructure consists of an α matrix in which inclusions of β phase in a proportion of from 5 to 45% by volume and of iron-nickel-manganese-containing mixed silicides in a proportion of up to 20% by volume are present, in that the iron-nickel-manganese-containing mixed silicides having a rod-like form and iron-nickel-enriched mixed silicides having a globular shape are present in the microstructure.
 2. The electrical connection element as claimed in claim 1, characterized by: from 30.0 to 36.0% of Zn, from 0.6 to 1.1% of Si, from 1.5 to 2.2% of Mn, from 0.2 to 0.7% of Ni, from 0.5 to 1.0% of Al, from 0.3 to 0.5% of Fe.
 3. The electrical connection element as claimed in claim 2, characterized by: from 33.5 to 36.0% of Zn.
 4. The electrical connection element as claimed in claim 1, characterized in that the electrical conductivity of the alloy is at least 5.8 MS/m.
 5. The electrical connection element as claimed in claim 4, characterized in that the electrical conductivity of the alloy is at least 10 MS/m.
 6. The electrical connection element as claimed in claim 5, characterized in that the electrical conductivity of the alloy is at least 13 MS/m.
 7. The electrical connection element composed of a copper-zinc alloy as claimed in claim 1, characterized in that the microstructure consisting of an α matrix in which inclusions of β phase in a proportion of from 5 to 45% by volume and of iron-nickel-manganese-containing mixed silicides in a proportion of up to 20% by volume are present has been formed after a further treatment comprising at least one hot forming and/or cold forming step and optionally further heat treatment steps.
 8. The electrical connection element composed of a copper-zinc alloy as claimed in claim 7, characterized in that the alloy has gone through the following steps during its further treatment: extrusion or hot rolling in the temperature range from 600 to 800° C., at least one cold forming step.
 9. The electrical connection element composed of a copper-zinc alloy as claimed in claim 7, characterized in that the alloy has gone through the following steps during its further treatment: extrusion or hot rolling in the temperature range from 600 to 800° C., a combination of at least one cold forming step and at least one heat treatment in the temperature range from 250 to 700° C.
 10. The electrical connection element composed of a copper-zinc alloy as claimed in claim 8, characterized in that, during the further treatment, the forming is followed by at least one annealing heat treatment in the temperature range from 250 to 450° C. 